4M40/ 4M41: Left Hand Thread Camshaft Bolts:

1994 – 2018  Mitsubishi Pajero 2.8L / 3.2L

2006 – 2009 Mitsubishi Triton 3.2L

1995 – 2004 Mitsubishi Delica 2.8L


All Head Services has a recurring problem of customers destroying camshafts and either stripping threads or shearing camshaft sprocket bolts on Mitsuibishi 4M40 and 4M41 engines.  This is caused by the fact that these bolts have a left hand thread.


In the July 2018 issue of Tech Talk (page 4536) we discussed the typical applications of left hand threads and how they are marked.  The convention for identifying a nut or bolt with a left hand thread is with grooves cut into the corners of the hexagon.  However, Mitsubishi have gone their own way.


The camshaft bolts on the 4M40 and 4M41 engines have an arrow cast into the head of the bolt to indicate the tightening direction, which in this case is anti-clockwise.


When these black bolts are covered in black and possibly sludgy diesel oil, these arrows cannot be seen and the bolts do not have the grooves cut into the corners of the hexagon to make it evident that they are a left hand thread.  As a result, technicians are applying excessive torque in the wrong direction to try and undo the bolts which is leading to expensive damage.


If you have been using a rattle gun on these bolts, then realise that you are turning them the wrong way, it is recommended that you replace the bolts, as is it is highly likely that you have streteched the bolt beyond its yield point.


When loosening or tightening the camshaft bolts on these engines, you should hold the camshaft with an open-ended spanner on the hexagon part of the camshaft.  Do not use the timing chain to hold the camshaft as you could damage components or skip teeth.  The torque specifications for these camshaft bolts are:

4M40: 90 Nm

4M41: 88 Nm


Using a left hand thread on the camshaft sprocket is rare and using an arrow on the end of the bolt to identify it is unconventional.  This is another trap to remember when working on these engines.

AHS recently had contact from a customer who had purchase a Nissan Patrol TB42 cylinder head, and after fitting had a complaint of oil in the cooling system.  The cylinder head had been on the vehicle for seven months and had only travelled 2000km.  The vehicle was dual fuel with petrol and LPG.  The cylinder head was removed and sent back to AHS, along with the head gasket

Upon inspection, the head was found to be bent .010″ with the obvious cause being severe detonation (which is uncontrolled combustion).  This had melted the cylinder head around the combustion chamber fire ring area, leading to the head gasket failure, which is how the oil got into the coolant.

With some further investigation, it was discovered that the LPG system on the vehicle was in an unserviceable condition and the owner was instructed to only run it on petrol until the LPG system was fixed. This advice was ignored.

LPG provides a hotter environment in the combustion chamber, which in turn increases the temperature of the cylinder head and if you add detonation into the mix, the head can melt.  In this case, the out of tune LPG system was found to be the cause of the detonation issues and the damage to the engine.

It is imperative with any fuel system and critical with LPG that the engine is kept in tune.  Detonation can be cause by many things, but incorrect ignition timing, ignition advance curve and air/fuel ratio are some of the main culprits.  Duel fuel applications add an extra complication due to the different characteristics of petrol and LPG.

At low rpm, the LPG burn rate is slower, so more ignition advance is needed, at high rpm the LPG burn rate is faster, so less advance is required.

Both of these are the opposite of the requirements of petrol, which can then increase the chance of detonation if the advance curve is not recalibrated.  Also if the air/fuel ratio is too lean, this will increase the speed and temperature of combustion, which again rises the change of detonation.

The customer stated that there was no damage to the bottom end of the engine.  This is lucky, as detonation can easily damage pistons, rings and bearing if it is left unchecked.  AHS were able to repair the cylinder head and returned it to the customer.





AHS has seen first-hand the vast amounts of carbon build up in the intake manifold and ports when rebuilding diesel engines with EGR Systems on them.

The build-up of carbon in crankcase oil has been a problem for some time, but with common rail engines, usually turbocharged and fitted with EGR valves, carbon is building up in the inlet tract at an alarming rate in some engines.

The carbon build up is caused when “Blow-By” gasses with suspended oil particles from the PVC (Positive Crankcase Ventilation) Valve and exhaust gases from the Exhaust Gas Recirculation (EGR) valve full of soot meet in the intake system. They then combine into a wet sticky mess which slowly builds up on the surfaces of the intake manifolds, intake ports and valves.  Short trips around town and low-temperature operation seem to make the build-up worse, high temperature and highway operations seem not to have this problem as much.

Over time this build up can turn hard and brittle which can break off and pass into the combustion chamber and become wedged in the piston ring lands or get lodged between the piston crown and valves or cylinder head.

This carbon build up must be removed completely from the intake system when either rebuilding the engine or replacing the cylinder head. Failure to do so could lead to engine damage or at least reduced performance.

There are not many shortcuts to carbon removal. Use a hot wash only on metal manifolds without plastic brushes for variable intake valves. A hot wash can damage plastic manifolds and internal parts.

Subaru SA459 Upper Cylinder Engine Cleaner seems to be the best product to loosen the carbon deposits.  Then use a bottle brush to get into the tight places.  See the March 2017 issue of Tech Talk and article on cleaning intake manifolds.

To avoid engine damage ensure that the manifolds and ports are meticulously cleaned prior to the engines assembly.

All Head Services recently had a VW Tiguan 1.4L TSI “Twincharger’ CAVD engine sent in for a rebuild due to low compression on number two cylinder.  The engine was dismantled for inspection, and number two cylinder’s piston rings had worn through the ring land of the piston, and the other three pistons had cracks in the ring lands.

These 1.4L TSI Twincharger engines are based on the EA111 engine family. They were designed on the idea of ‘downsizing’ in which a powerful and very efficient smaller capacity engine can do the same jobs as a larger less efficient engine while consuming less fuel.  In this case with a combination of supercharging, turbocharging and direct fuel injection.  These engines have won the award for best engine in the 1.0L to 1.4L class from 2006 to 2014 and was awarded the best overall International Engine of the year for 2009.  (See Tech Talk July 2007 page 2597 for system overview).

They are used in Volkswagen, Golf, Jetta, Scirocco, Tiguan, EOS, Polo and Passat.  Also the Audi A3, Seat Leon and the Skoda Octavia from 2005 to 2013. They have engine I.D. codes starting with CAV or CTH. However, trouble was coming.

The piston issue surfaced early, and Volkswagen started a service campaign (24S4) in 2010 to reduce its occurrence.  It involved reprograming the ECU with recalibrated settings for the knock sensor.  This may have been helpful; however, there was another problem that Volkswagen could not control.

These engines are designed to run on 95 RON unleaded petrol RON stands for Research Octane Number and the higher octane fuel allows the engine to compress the air/fuel mix to a higher compression ratio before detonation occurs.  This makes the engine more efficient.  However, as you have noticed at the service station, the higher the octane rating, the more expensive the fuel gets.

If the owners of the vehicles run the engine on 91 RON fuel because it is cheaper at the pump, it will cause preignition, detonation or pinging, which are all different names for uncontrolled combustion in the combustion chamber. This is combustion which occurs too early which then tries to force the piston back down the cylinder while it is still on the way up on the compression stroke.

Uncontrolled combustion can occur without any audible noise or knocking from the engine. If it occurs for a prolonged period, it will cause the ring lands to crack, the rings will break, which then start to wear their way through the ring lands (as shown in the pictures).  The first signs of this problem will be some rough running, then misfire related codes, but by this time, the damage has been done. A compression test should be conducted to confirm the issue.

These small, high output engines have been designed to perform very well when all of their requirements are met. You should have a chat with your customers with these engines and encourage them to use 95 RON fuel, as recommended in their owner’s handbook.  Otherwise, the money they think they have saved by buying cheaper fuel, probably will not cover the cost of a rebuilt engine.


All Head Services receive regular calls from customers with Multi-Layer Steel (MLS) head gasket sealing issues. This is despite continual technical articles and information being provided regarding the extreme importance of the head gasket surface area needing to be in the correct condition for MLS gaskets to have any chance of sealing. 

MLS gaskets cannot confirm to surface irregularities outside of their specifications, usually 20-30 Ra or Less. RA stands for “Roughness Average” which is the average measurement of peak-to-valley roughness height of a ‘flat’ surface.  The lower the Ra number, the smoother the surface.  Air powered whizzy discs tend to severely damage the gasket surface, by increasing the Ra number, especially on aluminium cylinder blocks.  This will inevitably lead to head gasket leakage and engine failure.

For the average workshop it is recommended to clean the block surface with a spray on gasket cleaner, then a plastic razor blade, then sharp steel razor blade held at 90 degrees to the block which should remove all of the old gasket material.  Then sand the surface with ultra-fine wet and dry paper on a flat sanding block to produce a polished finish.

Aluminium cylinder block gasket surfaces can warp if the engine is severely overheated. Once clean it is recommended to measure the block surface with a flat edge and feeler gauges. The popular rule of thumb is that the combined surface flatness of the head and the block should never exceed the number of cylinders on each bank across the length of the head / block when measured in thousandths of an inch (eg. 3 cylinders = .003″ (0.076mm), 4 cylinders= .004″ (0.102mm), and so on). The measurement across the head or block should not exceed .002″ (0.051mm). If the block surface is out of specification, it will need to be machined or replaced.

There is also the continual use of additional sealants (eg. Hylomer etc.) on the gasket surfaces which will cause the head gasket to leak.  MLS head gaskets already have a sealant applied, and any additional sealant coatings will stop the gaskets from working as it has been designed and it will fail to seal.

I cannot stress enough the importance of block preparation and following of the gasket manufacturer’s instructions when fitting MLS head gaskets to alleviate any chance of failure down the track.  If you have any questions on this topic refer to the Jan/Feb 2017 issue of Teck Talk or contact your gasket supplier.


All Head Services sold a customer a set of heads for a VZ V6 Alloytec engine and the customer fitted the heads, and also fitted new timing chain kit while it was apart. When the engine was started, there were no rattles, but the low oil pressure warning came up on the dash display.

A master oil pressure gauge was fitted, and the engine was showing ZERO oil pressure at idle (should be 69 kPa / 10 psi) and 40 psi when revved to 2000 RPM.  The oil pick up was checked with a camera and was clean (the pickups tend to block if the oil becomes sludgy) so the timing cover was removed and the components inspected.

The engines have three timing chains and three timing chain tensioners.  These tensioners are hydraulically actuated via pressurized oil from the engines lubrication system. This keeps the chain slack to a minimum and allows for automatic adjustment. Each tensioner also has an oil jet that sprays oil onto the chains while the engine is running.

All of the tensioners have a small oil reservoir between their body and their mating surface, this allows for quiet and fast operation on start-up. This reservoir of oil is contained by the rubber covered metal gaskets that seals the tensioners to the block or heads.  As this engine was dismantled and the timing chain tensioners removed, it was found that one the tensioners had not had the metal gasket fitted when it was being assembled. This was where the oil pressure was escaping. A new set of gaskets was fitted to the tensioners and the engine was reassembled. The engine had full oil pressure at idle and through the rev range.

As this case shows, one small component can reduce the oil pressure in the entire engine. The lesson from this is to make sure to replace all gaskets on reassembly, and not to assume that because a component is inside the engine that it does not need a gasket or to seal correctly.

The procedure to replace the timing chains on these engines is complicated, requires special tools and must be completed in two stages for the cam timing to be correct.